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Title: The Role of Specific Ion Effects in Ion Transport: The Case of Nitrate and Thiocyanate

Abstract

The selective transport of trivalent rare earth metals from aqueous to organic environments with the help of amphiphilic "extractants" is an industrially important process. When the amphiphilic extractant is positively charged or neutral, the coextracted background anions are not only necessary for charge balance but also have a large impact on extraction efficiency and selectivity. In particular, the opposite selectivity trends observed throughout the lanthanide series in the presence of nitrate and thiocyanate ions have not been explained. To understand the role of background anions in the phase transfer of lanthanide cations, in this work we use a positively charged long-chain aliphatic molecule, modeling a common extractant, and gain molecular level insight into interfacial headgroup-anion interactions. By combining surface sensitive sum frequency generation spectroscopy with X-ray reflectivity and grazing incidence X-ray diffraction, we observed qualitative differences in the orientational and overall interfacial structure of nitrate and thiocyanate solutions at a positively charged Langmuir monolayer. Though nitrate adsorbs without dramatic changes to the solvation structure at the interface or the monolayer ordering, thiocyanate significantly alters the water structure and reduces monolayer ordering. We suggest that these qualitatively different adsorption trends help explain a reversal in system selectivity toward lighter or heaviermore » lanthanides in solvent extraction systems in the presence of nitrate or thiocyanate anions.« less

Authors:
 [1];  [1];  [2]; ORCiD logo [1]
  1. Argonne National Lab. (ANL), Argonne, IL (United States)
  2. Univ. of Chicago, IL (United States). NSF’s ChemMatCARS
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division; National Science Foundation (NSF)
OSTI Identifier:
1606542
Grant/Contract Number:  
AC02-06CH11357; NSF/CHE-1834750
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 124; Journal Issue: 1; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Monolayers; Lanthanides; Interfaces; Anions; Ions

Citation Formats

Lovering, Kaitlin, Nayak, Srikanth, Bu, Wei, and Uysal, Ahmet. The Role of Specific Ion Effects in Ion Transport: The Case of Nitrate and Thiocyanate. United States: N. p., 2019. Web. https://doi.org/10.1021/acs.jpcc.9b09288.
Lovering, Kaitlin, Nayak, Srikanth, Bu, Wei, & Uysal, Ahmet. The Role of Specific Ion Effects in Ion Transport: The Case of Nitrate and Thiocyanate. United States. https://doi.org/10.1021/acs.jpcc.9b09288
Lovering, Kaitlin, Nayak, Srikanth, Bu, Wei, and Uysal, Ahmet. Wed . "The Role of Specific Ion Effects in Ion Transport: The Case of Nitrate and Thiocyanate". United States. https://doi.org/10.1021/acs.jpcc.9b09288. https://www.osti.gov/servlets/purl/1606542.
@article{osti_1606542,
title = {The Role of Specific Ion Effects in Ion Transport: The Case of Nitrate and Thiocyanate},
author = {Lovering, Kaitlin and Nayak, Srikanth and Bu, Wei and Uysal, Ahmet},
abstractNote = {The selective transport of trivalent rare earth metals from aqueous to organic environments with the help of amphiphilic "extractants" is an industrially important process. When the amphiphilic extractant is positively charged or neutral, the coextracted background anions are not only necessary for charge balance but also have a large impact on extraction efficiency and selectivity. In particular, the opposite selectivity trends observed throughout the lanthanide series in the presence of nitrate and thiocyanate ions have not been explained. To understand the role of background anions in the phase transfer of lanthanide cations, in this work we use a positively charged long-chain aliphatic molecule, modeling a common extractant, and gain molecular level insight into interfacial headgroup-anion interactions. By combining surface sensitive sum frequency generation spectroscopy with X-ray reflectivity and grazing incidence X-ray diffraction, we observed qualitative differences in the orientational and overall interfacial structure of nitrate and thiocyanate solutions at a positively charged Langmuir monolayer. Though nitrate adsorbs without dramatic changes to the solvation structure at the interface or the monolayer ordering, thiocyanate significantly alters the water structure and reduces monolayer ordering. We suggest that these qualitatively different adsorption trends help explain a reversal in system selectivity toward lighter or heavier lanthanides in solvent extraction systems in the presence of nitrate or thiocyanate anions.},
doi = {10.1021/acs.jpcc.9b09288},
journal = {Journal of Physical Chemistry. C},
number = 1,
volume = 124,
place = {United States},
year = {2019},
month = {12}
}

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